Many nurse practitioners say restrictive payment policies impact how they care for patients more than state laws governing what care they can give, according to a new study.

In the study, published Thursday by the National Institute for Health Care Reform, researchers found that while so-called “scope of practice” laws did not appear to restrict the primary care services nurse practitioners can provide to patients, they do affect how the advanced nurses are paid.

Researchers at the Center for Studying Health System Change conducted telephone interviews with 30 nurse practitioners, practice managers, and physicians working in a variety of clinical settings — all of which employed nurse practitioners. The researchers focused on six states representing a range of legal scope-of-practice restrictions: Maryland, Arizona, Michigan, Indiana, Massachusetts, and Arkansas.

Based on the interviews, Dr. Tracy Yee and her colleagues found that nurse practitioners — registered nurses with advanced degrees — faced greater challenges in the states with more restrictions on how they practice. In states such as Arkansas and Indiana where they cannot practice without a doctor’s supervision, nurse practitioners are not recognized as primary care providers by the traditional Medicaid program, and that affects how they deliver care to patients as well as how they are paid.

Other challenges in more restrictive states include disentangling the billing system involving public and private payers, ordering tests and procedures, and establishing independent primary care practices. And though private and public payers must adhere to scope-of-practice laws, they often impose additional restrictions on how these nurse practitioners practice, the study found.

Many nurse practitioners told researchers that restrictive payment policies had a much greater impact on their day-to-day practice than the current scope-of-practice laws enacted in their states. “Payers are in a position to determine what services NPs are paid for, their payment rates, whether NPs are designated as primary care providers and assigned their own patient panels, and whether NPs can be paid directly,” the authors of the study wrote.

Such policies “might hamper the efficiency of our provider capacity,” Yee said. “NPs can be doing more; they could be seeing more patients; they could be reaching communities that are underserved more often.”

States might consider making clearer what nurse practitioners can and can’t bill for — particularly in Medicaid and from other private payers, Yee added.

Dr. Angela Golden, president of the American Association of Nurse Practitioners, says she wasn’t surprised by the study’s findings on scope-of-practice laws. “It’s really important for people to recognize that removing those outdated laws will especially help people in medically underserved areas,” she said. “Fifty-five million people live in medically underserved areas.”

But Dr. Reid Blackwelder, the president-elect of the American Academy of Family Physicians, said he believes a more collaborative approach among physicians, advanced practice nurses, and physician assistants would pay dividends. “This discussion is often tied to the concept that an [advanced practice nurse] does what a family physician does or takes the place of a family physician. … What’s really important is that these roles are not interchangeable — they’re different,” he said during an interview. “Each is critical and each has a role to play. You can’t just take one and make due if you can’t have the other.”